Effects of ortho-Linkages on the Molecular Stability of Organic Light-Emitting Diode Materials

Abstract

ortho-Linkages are effective in improving the performance of organic light-emitting diode (OLED) materials but may weaken the local chemical bonds and even incur chemical degradation due to bond cleavage reactions in operating OLEDs, especially for blue-emitting materials. Here, we conducted a systematic theoretical study on a series of carbazole (Cz)-based molecules with typical donor (D)−π−acceptor (A) structures to investigate the influence of ortho-substituents on the bond dissociation energies (BDEf) of their fragile D−π bonds (i.e., C–N bonds), where “fragile” means that the bonds have the minimum or a comparable-to-the-minimum BDE in the molecule. Through calculations, it was found that different substituents or even the same substituent on different sites of the molecule could bring variable effects on the polar D−π bond. Specifically, in the π-group, the effects of a substituent on BDEf mainly depend on the steric hindrance that it brings to the D−π bond. Thus, ortho-CH3 groups hardly affect BDEf...